The present invention relates to a method for controlling the regenerative braking of an electrically powered vehicle or a vehicle with hybrid combustion engine/electric power. In the case of hybrid vehicles for example, it known practice to apply the motive or driving force of the combustion engine to a first axle system and to apply the motive force of an electric motor to a second axle system of the vehicle. In the case of an all-electric vehicle, the vehicle can be set in motion by a single motor connected, for example, to one axle system of the vehicle or by several motors, for example one motor per axle system of the vehicle, or a motor associated with each wheel. All of the engines and/or motors devoted to propulsion (on the front axle system and on the rear axle system) of the vehicle together with all the associated transmission components (clutches, gearboxes) will be termed PT (for Power Train). In the prior art, it is also known practice, when there is an electric machine acting as a motor to drive the vehicle, for this motor to be operated in a regenerative braking mode, that is to say that, from an electrical standpoint, this machine, which then works like a generator, converts the mechanical energy applied to its rotor into an electric current that can then be regulated in an electric machine controller as a current used to charge an electric battery. In this mode of operation, the consumption of mechanical energy produced by the electrical conversion applies a braking torque to the wheels of the vehicle. This means firstly that the vehicle can be at least partially braked using the electric drive machine operating as a generator, and secondly that the kinetic energy recovered by the braking action can be stored in electrical form in a bank of accumulator cells or battery, this energy being reusable subsequently to propel the vehicle or for ancillary functions. Regenerative braking can be used during actual braking phases, that is to say when the driver presses the brake pedal. This regenerative braking has been developed to work for preference during braking-free deceleration phases, namely when the driver “lifts his foot off” the throttle pedal, without operating the brake pedal. A “neutral point” can thus be defined in the travel of the throttle pedal, as being the point at which the torque transmitted to the wheels by the PT is zero. Beyond the neutral point, the PT supplies the driven wheels with a motive torque. Short of the neutral point, the PT applies a resistive torque to the driven wheels. This resistive torque may be entirely (give or take efficiency losses) converted into electrical energy in the case of an all-electric vehicle. In the case of a hybrid vehicle, this resistive torque can be split into torque generated by the engine braking (due to friction of the mechanical parts, notably of the pistons in the cylinders of the combustion engine) and into a regenerative braking toque which is converted into electricity by the electric motor.
The amount of regenerative braking to be used depends on the kinetic energy available, and therefore on the speed of the vehicle, on the converted electrical energy that the vehicle can absorb by direct consumption or by storage in a battery. In order to take these variations into consideration, patent application US 2006/137925 proposes using a computer to modify the motive or resistive torque values associated with the various positions of the throttle pedal (which will in the remainder of the text be simply termed the “pedal”), the modification being made as a function of the mode of operation of an electric or hydraulic regenerative device. The solution proposed is expensive to implement because it assumes the installation of a special-purpose computer inserted between the pedal and the PT, and wiring from the computer to the pedal, the regenerative system and the PT. The document does not specify how drivability is taken into consideration in the modifications to the way in which the pedal behaves.
Further, the batteries of a vehicle cannot be recharged beyond their maximum charge level. The level of regenerative braking has therefore to be limited as the battery gradually approaches its fully charged level, and this regenerative braking has to be increased again when the battery charge decreases. The document does not propose how to manage these variations as a function of battery charge level either.